Efficient power amplifier

Abstract

A dynamic power supply for N amplifiers includes first and second power boost circuits which temporarily boost the positive or negative power supply rail, respectively. A control circuit monitors amplifier output signal levels and provides power boost control signals to the power boost circuits, which temporarily raise the positive supply voltage above the nominal voltage level in tandem with the highest output signal from the N amplifiers and lower the negative supply voltage below the nominal voltage level in tandem with the lowest output signal level from the N amplifiers. The power boost circuits each may be coupled to a reservoir capacitor from which current is drawn to provide the power boost. When inactive, the reservoir capacitors charge up from the respective power supply rails. The dynamic power supply is well suited for audio amplification systems.

What is claimed is: 
     
       1. A dynamic amplification system for a plurality of amplifiers, comprising:
 a first amplifier coupled to a first input signal for amplification and operative to generate a first output signal; 
 a second amplifier coupled to a second input signal for amplification and operative to generate a second output signal; 
 a first power boost amplifier electrically connected to a first power supply rail, said first power supply rail providing power at a first nominal voltage level to the first and second amplifiers; 
 a second power boost amplifier electrically connected to a second power supply rail, said second power supply rail providing power at a second nominal voltage level to the first and second amplifiers; 
 a power boost control circuit; 
 a first gain stage operative to generate a modified version of the first input signal and provide the modified version to the power boost control circuit; and 
 a second gain stage operative to generate a modified version of the second input signal and provide the modified version to the power boost control circuit; 
 wherein said power boost control circuit is operative to provide power boost control signals to said first power boost amplifier and said second power boost amplifier, whereby said first power boost amplifier temporarily boosts the first power supply rail above the first nominal voltage level in tandem with the highest output signal level from said first and second amplifiers as indicated by said modified versions of said first and second input signals, and whereby the second power boost amplifier temporarily lowers the second power supply rail below the second nominal voltage level in tandem with the lowest output signal level from said first and second amplifiers as indicated by said modified versions of said first and second input signals. 
 
     
     
       2. The dynamic amplification system of  claim 1 , wherein said modified versions of the first and second input signals are indicative of signal levels of the first and second output signals respectively from the first and second amplifiers. 
     
     
       3. The dynamic amplification system of  claim 2 , wherein the first gain stage is matched to a gain of the first amplifier, and wherein the second gain stage is matched to a gain of the second amplifier. 
     
     
       4. The dynamic amplification system of  claim 2 , wherein said power boost controller is operative to cause said first power boost amplifier to raise the first power supply rail above the first nominal voltage level when the highest output signal level, as indicated by said modified versions of said first and second input signals, approaches the first nominal voltage level within a first predefined margin, and wherein said power boost controller is operative to cause said second power boost amplifier to lower the second power supply rail below the second nominal voltage level when the lowest output signal level, as indicated by said modified versions of said first and second input signals, approaches the second nominal voltage level within a second predefined margin. 
     
     
       5. The dynamic amplification system of  claim 4 , wherein said first nominal voltage level and said second nominal voltage level have the same magnitude but opposite polarity, and wherein said first predefined margin and said second predefined margin have the same magnitude. 
     
     
       6. The dynamic amplification system of  claim 4 , wherein said power boost controller is operative to cause said first power boost amplifier to maintain the first power supply rail above the highest output signal level from said amplifiers by approximately said first predefined margin when said first power boost amplifier is active, and to cause said second power boost amplifier to maintain the second power supply rail below the lowest output signal level from said amplifiers by approximately said second predefined margin when said second power boost amplifier is active. 
     
     
       7. The dynamic amplification system of  claim 1 , further comprising:
 a first reservoir capacitor; 
 a second reservoir capacitor; 
 wherein said first power boost amplifier draws current from said first reservoir capacitor when active to boost the first power supply rail above the first nominal voltage level; and 
 wherein the second power boost amplifier draws current from said second reservoir capacitor when active to lower the second power supply rail below the second nominal voltage level. 
 
     
     
       8. The dynamic amplification system of  claim 7 , wherein said first reservoir capacitor is coupled to the first power supply rail via a first diode thereby permitting said first reservoir capacitor to charge when not actively boosting power to said amplifiers, and wherein said second reservoir capacitor is coupled to the second power supply rail via a second diode thereby permitting said second reservoir capacitor to charge when not actively boosting power to said amplifiers. 
     
     
       9. The dynamic amplification system of  claim 1 , further comprising:
 a first voltage sense circuit operative to monitor the first power supply rail feeding the first and second amplifiers; and 
 a first variable offset circuit responsive to said first voltage sense circuit operative to inject a first variable feedback signal into said first power boost amplifier, said first variable feedback signal proportional in magnitude to a voltage level of the first power supply rail. 
 
     
     
       10. The dynamic amplification system of  claim 9 , further comprising:
 a second voltage sense circuit operative to monitor the second power supply rail feeding the first and second amplifiers; and 
 a second variable offset circuit responsive to said second voltage sense circuit operative to inject a second variable feedback signal into said second power boost amplifier, said second variable feedback signal proportional in magnitude to a voltage level of the second power supply rail. 
 
     
     
       11. A dynamic amplification system, comprising:
 a power boost circuit comprising a power boost amplifier electrically coupled to a power supply rail, said power supply rail providing power at a nominal voltage level to a plurality of amplifiers receiving a plurality of input source signals, each amplifier operative to receive one of said input source signals and to provide an output signal; and 
 a plurality of gain stages each coupled to one of said input source signals and outputting a modified version of its corresponding input source signal to the power boost circuit; 
 wherein said power boost amplifier temporarily boosts the power supply rail above the nominal voltage level in tandem with the highest output signal level from said amplifiers as indicated by the modified versions of said input source signals. 
 
     
     
       12. The dynamic amplification system of  claim 11 , wherein each gain stage is matched to a gain of the amplifier receiving the same input source signal as the gain stage. 
     
     
       13. The dynamic amplification system of  claim 11 , wherein said power boost amplifier is operative to raise the power supply rail above the nominal voltage level when the highest output signal level, as indicated by the modified versions of said input source signals, approaches the nominal voltage level within a predefined margin. 
     
     
       14. The dynamic amplification system of  claim 13 , wherein power boost amplifier is operative to maintain the power supply rail above the highest output signal level from said amplifiers by approximately said predefined margin when said power boost amplifier is active. 
     
     
       15. The dynamic amplification system of  claim 13 , further comprising an energy source providing a charge reservoir, wherein said power boost amplifier draws current from said charge reservoir when active to boost the power supply rail above the nominal voltage level. 
     
     
       16. The dynamic amplification system of  claim 11 , further comprising:
 a voltage sense circuit operative to monitor the power supply rail; and 
 a variable offset circuit responsive to said voltage sense circuit operative to inject a variable feedback signal into said power boost amplifier, said variable feedback signal proportional in magnitude to a voltage level of the power supply rail. 
 
     
     
       17. A dynamic amplification system, comprising:
 a first power boost amplifier electrically coupled to a first power supply rail, said first power supply rail providing power at a first nominal voltage level to a plurality of amplifiers, each amplifier having an input to receive an input source signal and an output to provide an output signal; 
 a second power boost amplifier electrically coupled to a second power supply rail, said second power supply rail providing power at a second nominal voltage level to the plurality of amplifiers; and 
 a power boost control circuit, said power boost control circuit configured to monitor indicia of the output signal levels for the amplifiers, and to selectively provide power boost control signals to said first power boost amplifier and said second power boost amplifier; 
 whereby said first power boost amplifier temporarily boosts the first power supply rail above the first nominal voltage level in tandem with a highest output signal level from among said amplifiers approaching or exceeding a first threshold, and whereby the second power boost amplifier temporarily lowers the second power supply rail below the second nominal voltage level in tandem with a lowest signal level from among said amplifiers approaching or exceeding a second threshold. 
 
     
     
       18. The dynamic amplification system of  claim 17 , further comprising a plurality of gain stages, each gain stage coupled to one of the input source signals of said amplifiers, said gain stages configured to output modified versions of said input source signals indicative of the output signal levels of said amplifiers to the power boost control circuit. 
     
     
       19. The dynamic amplification system of  claim 18 , wherein each gain stage is matched to a gain of the amplifier receiving the same input source signal as the gain stage. 
     
     
       20. The dynamic amplification system of  claim 17 , further comprising:
 a first stored energy source providing a first charge reservoir; 
 a second stored energy source providing a second charge reservoir; 
 wherein said first power boost amplifier draws current from said first stored energy source when active to boost the first power supply rail above the first nominal voltage level; and 
 wherein the second power boost amplifier draws current from said second stored energy source when active to lower the second power supply rail below the second nominal voltage level. 
 
     
     
       21. The dynamic amplification system of  claim 20 , wherein said first stored energy source comprises a first reservoir capacitor coupled to the first power supply rail via a first diode thereby permitting said first reservoir capacitor to charge when not actively boosting power to said amplifiers, and wherein said second stored energy source comprises a second reservoir capacitor coupled to the second power supply rail via a second diode thereby permitting said second reservoir capacitor to charge when not actively boosting power to said amplifiers. 
     
     
       22. The dynamic amplification system of  claim 17 , wherein said first nominal voltage level and said second nominal voltage level have the same magnitude but opposite polarity. 
     
     
       23. An amplification system, comprising:
 a first power boost circuit coupled to a first power supply rail, said first power supply rail providing power at a first nominal voltage level to a plurality of amplifiers, each amplifier operative to receive an input source signal and to provide an output signal; 
 a second power boost circuit coupled to a second power supply rail, said second power supply rail providing power at a second nominal voltage level to the plurality of amplifiers; 
 a first voltage sense circuit operative to monitor the first power supply rail; and 
 a first variable offset circuit responsive to said first voltage sense circuit operative to inject a first variable feedback signal into said first power boost amplifier, said first variable feedback signal proportional in magnitude to a voltage level of the first power supply rail; 
 wherein said first power boost amplifier is operative to temporarily boost the first power supply rail above the first nominal voltage level in tandem with the highest output signal level from said amplifiers, and wherein said second power boost amplifier is operative to temporarily lower the second power supply rail below the second nominal voltage level in tandem with the lowest output signal level from said amplifiers. 
 
     
     
       24. The amplification system of  claim 23 , further comprising:
 a second voltage sense circuit operative to monitor the second power supply rail; and 
 a second variable offset circuit responsive to said second voltage sense circuit operative to inject a second variable feedback signal into said second power boost amplifier, said second variable feedback signal proportional in magnitude to a voltage level of the second power supply rail. 
 
     
     
       25. The amplification system of  claim 24 , wherein said first power boost amplifier is operative to raise the first power supply rail above the first nominal voltage level when the highest output signal level approaches the first nominal voltage level within a first predefined margin, and wherein said second power boost amplifier is operative to lower the second power supply rail below the second nominal voltage level when the lowest output signal level approaches the second nominal voltage level within a second predefined margin. 
     
     
       26. The amplification system of  claim 24 , wherein said first nominal voltage level and said second nominal voltage level have the same magnitude but opposite polarity. 
     
     
       27. The amplification system of  claim 24 , wherein first power boost amplifier is operative to maintain the first power supply rail above the highest output signal level from said amplifiers by approximately said first predefined margin when said first power boost amplifier is active, and wherein said second power boost amplifier is operative to maintain the second power supply rail below the lowest output signal level from said amplifiers by approximately said second predefined margin when said second power boost amplifier is active. 
     
     
       28. The amplification system of  claim 24 , further comprising:
 a first reservoir capacitor; 
 a second reservoir capacitor; 
 wherein said first power boost amplifier draws current from said first reservoir capacitor when active to boost the first power supply rail above the first nominal voltage level; and 
 wherein the second power boost amplifier draws current from said second reservoir capacitor when active to lower the second power supply rail below the second nominal voltage level. 
 
     
     
       29. The amplification system of  claim 23 , further comprising a plurality of gain stages each coupled to one of said input source signals and outputting a modified version of its corresponding input source signal, each gain stage being matched to a gain of the amplifier receiving the same input source signal as the gain stage. 
     
     
       30. A method for amplification using independent positive and negative power supply rail boosting, comprising:
 directly or indirectly monitoring output signal levels of a plurality of amplifiers; 
 selecting the output signal level having a highest signal level from the output signal levels; 
 selecting the output signal level having a lowest signal level from the output signal levels; 
 providing the highest signal level to a first power boost circuit; 
 providing the lowest signal level to a second power boost circuit; and 
 selectively engaging said first power boost circuit and said second power boost circuit to temporarily boost positive and negative power supply input voltage levels to said amplifiers as the highest signal level and lowest signal level from said amplifiers approaches or exceeds a positive power supply rail or a negative power supply rail, respectively. 
 
     
     
       31. The method of  claim 30 , further comprising:
 receiving, at said first power boost circuit, a first feedback signal corresponding to the boosted positive power supply input voltage; 
 applying a first variable gain factor for said first power boost circuit's power boost function that increases as the positive power supply input voltage signal increases in magnitude; 
 receiving, at said second power boost circuit, a second feedback signal corresponding to the boosted negative power supply input voltage; and 
 applying a second variable gain factor for said second power boost circuit's power boost function that increases as the negative power supply input voltage signal increases in magnitude. 
 
     
     
       32. The method of  claim 31 , wherein the output signal levels of said plurality of amplifiers are monitored by coupling a gain stage to an input signal to each of the amplifiers, each gain stage having a gain matching that of the amplifier receiving the corresponding input signal, the output of each gain stage reflecting the output signal level of the corresponding amplifier. 
     
     
       33. The method of  claim 31 , wherein said first power boost circuit raises the positive power supply rail voltage above a first nominal voltage level when the highest output signal level approaches the first nominal voltage level within a first predefined margin, and wherein said second power boost circuit lowers the negative power supply rail voltage below a second nominal voltage level when the lowest output signal level approaches the second nominal voltage level within a second predefined margin. 
     
     
       34. The method of  claim 30 , wherein one of more of the amplifiers is coupled to an audio speaker and provides an audio output signal thereto.